Manufacture of gasoline



.June 1948. L. P. scovlLLE MANUFACTURE OF GASOLINE Filed Jan. l5, 1943 2YSheets-Sheet l NNZJFDmMD P. SCOVILLE VENTOR 'illy WO- NGC 596mm holtIii' INVENTOR 2 Sheets-Sheet 2 Ll wo a L. P. SCOVILLE MANUFACTURE OFGASOLINE `lume l, 1948.

Filed Jan. 15, 1943 LOREN P. SCOVILLE mwN. 24101@ wn.

WENT- mgm now A Patented June 1 1948 MANUFACTURE OF GASOLINE Loren P.Scoville, Yonkers, N. Y., assgnor to The Texas Company, New York, N. Y.,a corporation of Delaware Application January 15, 1943, Serial No.472,439

1 Claim. 1 This invention relates to the manufacture of gasoline, suchas aviation gasoline and motor fuel, from normally gaseous and liquidhydrocarfbons. More particularly, the invention relates to thestabilization and fractionation of refinery hydrocarbon fractions, suchas cracked naphtha and natural gasoline, and the catalytic conversion ofe'iuent low-boiling or normally gaseous hydrocarbons to gasolinehydrocarbons of high anti-knock value.

One of the principal objects of the invention is to provide an improvedprocess of stabilizing and fractionating petroleum products orfractions, such as cracked naphtha, and of converting low-boiling ornormally gaseous eilluents of such stabilization and fractionation togasoline hydrocarbons of high anti-knock value, to thereby increase theyields of aviation gasoline and motor fuel produced from availablerenery fractions, eliminate or minimize corrosion, and secure otheradvantages.

Another object of the invention is to provide a novel method oi"stabilizing and fractionating hydrocarbon mixtures to obtain a betterseparation of desired fractions, while at the same time providing ahigher stabilization pressure and a greater overhead condensate recoverywith available cooling water or other medium for the same reboilertemperature.

Still another object of the invention is to provide an improved methodof stabilizing and fractionating hydrocarbon mixtures containing bothparai'n'ns and olens of the same number of carbon atoms per molecule,whereby a portion of a Y normal paraiiin may be retained in thestabilized bottoms for volatility While electing a greater recovery ofthe olens of the same carbon atom content in the overhead.

Another object of the invention is t provide an improved method ofstabilizing raw cracked naphtha and polymerizing overhead low-boiling ornormally gaseous unsaturated hydrocarbons to polymer gasoline, wherein aportion of a W-boiling normal paraiiin is retained in the stabilizedcracked naphtha for volatility, while at the same time a greaterproportion of the oleiins of the same carbon atom content as thelow-boiling normal paraffin are removed in the overhead. to therebyincrease the yield of polymer gasoline,

Still another object of the invention is to provide an improved methodof stabilizing raw cracked naphtha and natural gasoline, and alkylatingoverhead low-boiling or normally gaseous isoparains with olens toproduce aviation gasoline, wherein a greater recovery of lowboilingolens and isoparalns is eiected from the raw cracked naphtha and thenatural gasoline to thereby materially increase the yield of aviationgasoline, While low-boiling normal paraln components are retained in thestabilized naphtha or gasoline for volatility. t

A further object of the invention is to provide apparatus for carryingout the method of this invention, Iwhich apparatus is simple inconstruction, is readily available and easily controlled, and economicalin operation and maintenance.

Other objects and advantages of the invention will be apparent from thefollowing description when taken in conjunction with the accompanyingdrawing and appended claim.

In the drawing which illustrates preferred embodiments of the invention:v

Fig. 1 is a diagrammatic illustration of apparatus for carrying out themethod of this 1nvention as applied to the stabilization of raw crackednaphtha and the polymerization of eiliuent gases therefrom; and Y i Fig.2 is a diagrammatic illustration of apparatus for carrying out themethod of this .1nvention as applied to a modication involving thestabilization and fractionation of raw cracked naphtha and naturalgasoline, and the alkylation of eilluent low-boiling or normally gaseousisoparaffins and olens therefrom.

In conventional renery practice, it 1s customary to stabilize rawcracked naphtha as obtained .from the cracking of petroleum hydrocarbonsto remove normal butane and lighter, the eilluent gases then beingtreated and converted in part to gasoline hydrocarbons of hlgh antlknockvalue by various processes including polymerization and alkylation. Theresulting conversion products are stabilized and fractionated to recoveran aviation gasoline, and a portion of the normal butane may be blendedback with the stabilized cracked naphtha for volatility. As applied topolymerization, it is customary to stabilize the raw cracked naphtha toremove overhead C4 and lighter. The overhead gases may then befractionated to separate a selected C4 fraction, and the resulting C4fraction is then polymerized to polymer gasoline, stabilized andhydrogenated to provide a saturated isoparafnic aviation gasoline, Onthe other hand, the overhead gases may be condensed, and the condensatecomprising mainly C3C4 hydrocarbons polymerized and stabilized to form ahigh octane motor gasoline. In an effort to secure maximum yields ofthis gasoline, the raw cracked naphtha may be deeply stabilized toremove substantially all of the normal butane and lighter, so thatpractically all of the C4 olens' are obtainedin' the'overhead. In thisvoperation, difficulties may be-encountered in condensing the desiredamount of overhead gases with the use of available cooling water withoutrefrigeration due to the lower stabilizer pressure required for a givenavailable reboiler temperature; and the increasedyield of polymerizableolens in the stabilizer4 overheadmaybe counterbalanced by the oleiinsremaining uncondensed and passing to the reiinery gaslines, rather thanbeing passed in the condensate to the polymerization unit. On th'e otherhand, if lthe stabilizer pressure is maintained constant, this deep.stabilization of the v:cracked naphtha re- ',quires a'higher reboilertemperatura-which may be .above Vthat normally obtainable -with the1available renery high pressure `Asteam supply. .-fAlso,-thedeep-stabilization lowers the front end .volatility of the stabilizedcracked naphtha-so :that it will not meet specificationsfor motorfuel,and necessitates the'blending back of normalrbu- .tane with-thestabilized cracked naphtha to meet -front end volatility specifications.

Consequently, in many refineries; a'compromise is eiected on the basisoi" the available Vhigh pressure steam supply and the'. availablezcooling Awa- 'ter temperaturebetween-thedeep stabilization of therawcracked .naphtha describedV aboveandl an operation in which asubstantial proportion of the C4 vhydrocarbons Vare left .in vthestabilized cracked naphtha forvolatility. Whilethis .latter operationretainsnormal butaneinthe stabilized `cracked naphtha, itis also-accompaniedzby a' substantial loss of the C4 olefins,particularlyzbutyl- `ene-2, in the stabilizer .'bottoms. Tlf'hisfresultsin a loss of desirable oleiins in the :polymer charge, with-a resultantdecrease in yield of aviation or motor gasoline 'from .thattheoretically possible from the available refinery stocks.

In order to operate ata suicientlyhigh stabilizer pressure to condensethe major portion of the desirable constituents of .the overhead'fromtheraw cracked naphtha stabilizer, it has 'been previously proopsed toinject water into the reboiler of the stabilizer, However, this methodisnecessarily limitedto anincrease in stabilizer pressure ofapproximately fiftypounds per square inch for a given reboilertemperature and', in addition, may ,result in increased corrosion.

.In .accordance with the present invention, `an improved method ofoperation .is provided for `stabilizing ther-aw cracked naphthadirectlyto desired volatility andR. V. P., while at the same .time -theportion -of C4 retained in the stabilizer lhottonls-consists largely-ofAnormal butane, and -a materially .increased .proportion of C4 olens forthe .particular relatively flow reboiler temperature Vused is securedinthe roverhead; Moreover, .this method at the same time enables .thestabilizer `operating pressure `to .be increasedsubstantially more thanthe above-noted'fifty pounds der v1a given reboiler temperature withoutthe use of water injection, whereby an increased recovery of thevaluable unsaturated hydrocarbons is obtained in the overhead condensateby the use of available cooling water, or the same recovery canAdrocarbon 'fraction may be introduced at any .point within the towerbelow the point of entry of the-normarreiiuX-condensate, but preferablyis added below :the vpoint of entry of raw cracked naphtha charge, Verygood results have been secured'byintroducing this saturated C4 recyclestreaminto the stabilizer reboiler.

The invention is more particularly illustrated in Fig. 1, which showstheraw cracked-naphtha -asbbtained from a renery cracking operation beingcharged. by pump l0 throughfline ll finto -an intermediatevpoint ofstabilizer I2. Thelatter maybe a conventional fractionating tower ofthemultple bubble plate type, andxisequipped with a line i3 forwithdrawingliquid. from a pool within the base oi thetower and passingthe same through a reboiler i4 heatedbyhigh pressure steam supplied toheating con-i5,.theheatedhydrocarbon being returned to the .base f ythetower by line I6. .A bottoms .of stabilized cracked naphtha is withdrawn.fromthebase of thetower by line ifi. Overhead.gases-composedrof-Cnandlighter pass by. line I8 Vto water-cooledfccndenser i9 and thencebyrundownline .20 tdaccumulator 2l. Uncondensedgas, mainly `C2 andlighter,-is bled off Afrom .accumulator :2l byV overheadY line '22 .toVsuitable gas-.collecting lmeans not shown.

Liquid condensate, .consisting largely ofCs-C, fis withdrawn from theaccumulatorthrough line 23and forced by ipump 24 lthrough'line 25. .Thelatter communicates `with-branched lines so that aportionofthe/condensatemay be returnedby line 21 to the upper-portionvof tower:I2 to serve as reflux therein, while another portion passes vby line28..to.a polymerization unitindicated generally at 29,

Any conventional catalytic or thermal polymerization vunit forconverting thelolefinic 'constituents of the-charge to polymerinay beemployed. Since the polymerization unit 'per se forms no part of thepresent invention, further illustration thereof is deemedunnecessary. Byway vof example, the unit 29 may bea conventionalphosphoric acid unitprovided with a-heater in which the charge is .raised to a temperatureof about 3504500" F. andthen passed through a catalytic tower orconverter containingkieselguhr on which is rabsorbed the'phosphoric:acid catalyst. The operation thus far described is .a so-caliednon-selective polymerization in which both C: and C4 olens arepolymerized in the presence of each other. However, it is'to beunderstood that the overhead condensate Lfrom the stabilizer l2 could befurther fractionated .to separate mainlya'C4 fraction, wherebycross-polymerization of .fnormalan'd isobutylenes :occurs in theunitiZS. 'In any Vevent,litiis' toibel understood that the C4 oleins ofthe charge are largely consumed in the polymerization step to formhigher boiling normally liquid polymers.

The resulting polymerization products are passed by line 3D to adepropanizer 3| where Cs and lighter are removed overhead by line 32 andthe depropanized polymer gasoline is withdrawn as bottoms by line 33.The overhead gas passes to condenser 34 and thence by rundown line 35 toan accumulator 36 from which condensate is withdrawn by line 3l andreturned by pump 38 through line 39 to an upper portion of tower 3| toserve as redux therein. It is also to be understood that thedepropaniz'er 3| may be equipped with a suitable heating coil orreboiler in the conventional manner.

The depropanized polymer gasoline passes by line 33 into a debutanizer49 also equipped with a conventional heating coil or reboiler at thebase of the tower (not shown), and from which a saturated C4 streamconsisting essentially of normal butane and isobutane is removed asoverhead by line 4| and a stabilized polymer gasoline is withdrawn asbottoms by line 42 for passage to motor gasoline storage or to ahydrogenator (not shown) in the case of selective polymerization in theproduction of aviation gasoline as is well understood. The saturated C4gases pass by line 4| to condenser 43 and run down line 44 to anaccumulator 45. The saturated C4 condensate is withdrawn fromaccumulator 45 by line 46 and forced by pump 41 in part through line 49to the top of tower 40 to serve as redux therein, and in part by line 49to the reboiler I4 of cracked naphtha, stabilizer |2 The amount ofsaturated C4 which is recycled through line 49 to stabilizer l2 can bevaried within substantial limits. For example, a relatively small amountof recycle on the basis of the raw cracked naphtha charged will giveimproved operation, and this can be varied up to the recycle ofsubstantially all of the saturated C4 condensate not required as refluxin debutanizer 49. Thus, a recycle rate of as little as one part byvolume f saturated C4 to a hundred parts by volume of raw crackednaphtha charged and up to equal parts by volume or more may be employed.In the latter case, it is obvious that additional saturated C4 from anexternal source would be required in initiating operation and untilthere had been substantial buildup of the saturated C4 in the system.Generally, about one part of saturated C4 to twenty parts by volume ofraw cracked naphtha charged up to one part of recycle to ten parts ofnaphtha charged are preferred to maintain the proper balance in thesystem. It will be understood that this will very for diierent reboilertemperatures and diilerent temperatures of available cooling water andcan readily be determined in actual operation by those skilled in thisart for the particular conditions encoun- '60 tered to provide the mostefficient operating conditions. In operation, the amount of recycle maybe controlled by any conventional rate of dow controller in accordancewith the rate of feed of the raw cracked naphtha to stabilizer l2. Thisis illustrated diagrammatically by ratio flow controller 50 between lineand line 49 with air connection regulating a valve 52 in recycle line49. It is to be understood that the hydrocarbon recycle can also becombined with direct water injection into the stabilizer tower, ifdesired. to obtain the cumulative effect on increase in tower pressurefor a given reboiler temperature of both the hydrocarbon injection andthe water injection.

'Ihe following results were obtained in comparative runs in commercialoperation on a combined `raw cracked naphtha stabilization operation anda polymerization of the stabilizer overhead condensate by a conventionalphosphoric acid polymerization process.. In one run, the raw crackednaphtha stabilizer was operated in conventional manner withouthydrocarbon recycle and injection into the reboiler of the stabilizer.In another run, a saturated C4 fraction obtained in the stabilization ofthe polymerization products as in Fig. 1 above was recycled at the rateof 14.6 B. P. H. into the reboiler of the raw cracked naphtha stabilizerto which the raw cracked naphtha was fed at the same rate as in theprevious run, namely, at about 208 B. P, H. The following were theconditions and results of the run: v

without b u- Btlmifw tme injection tane injected into reboiler intoreboler Rates in barrels per hour:

Charge to raw cracked napththa. 208 208 Butane injection into reboiler 014. 6 Charge to polymerization uni 45. 55 60. 98 Redux to stabilizertower 124. 45 131. 02 4Redux ratio 2. 3:1 2. 0:1 Stabilizer bottoms R.V. P. in lbs. 10. 1 10.5 Redux material-Dist. IBP F -44 5 Reduxmaterial-Dist. 98% od at.. +30 +34 Pressure, lbs. per sq. in. gauge:

Stabilizer tower top 215 212 Redux accumulator drum 211 208 Highpressure steam for reboiler 174 172 Temperature, F.:

Stabilizer tower top 136 146 Raw naphtha to tower 208 208 Reboiler vapor345 342 Redux accumulator drum.- 88 88 Water supply to condenser 8l 82Water discharged from condenser. 94

Charge plus butano recycle combined Liquid Vol. Per B. P. H.

cent Liquid,

Vol. Per B. P. H.

cent

Analysis Chg. to Stabilizer:

Methane 0.42 0. 87 0. 39 0.87 Ethylene 0. 73 l. 52 0.68 1.52 Ethane. 3.79 7.88 3. 54 7. 88 Propylene- 3. 77 7.84 3. 52 7. 84 Propane 6. 26 13.02 5. 85 13.02 Isobutane 2. 30 4. 78 3. 04 6. 76 Isobutylene+butylene-l. 3. 53 7. 34 3. 63 8. 09 Normal butan 6. 51 13. 54 10.00 22.25 Butylene-2 3. 71 7. 72 4. 57 l0. 18 PentoneS-l- 68. 98 143. 49 64. 78144. 19 Analysis butane recycle:

Isobutane 13. 58 1. 98 Isobutylene-lbutylene-l 5. 15 0. 75 Normal butano59. 64 8. 7l 16. 84 2. 46 4179 Y 0.70

2. 26 1. 03 1. 50 0. 91 4. 48 2.04 2.24 1. 36 9.54 4. 34 13. 90 8. 4811.30 5.15 13. 32 8.12 34 15. 19 28. 92 17. 63 Isobutane. 6. 35 2. 89 6.78 4. 13 lsobutylene+ butylene-l 8. 7l 3. 97 9. 66 5. 89 Normal butane15.91 7. 25 15.79 9.63 Butyle11e2 6. 71 3. 05 6. 49 3. 96 PentaDes-l- 1.40 0. 64 1. 40 0.85 Analysis stabilized bottoms:

Isobutane-l-normal b t 6. 73 6. 96 11.04 5. 78 2. 68 4. 25 PentaneS-i142.85 90. 36 143. 34

area/14o without bu- Bwltlifw tim-1e necio tane injected into reboilerma remuer Total Q4 in stabilizer charge B. P. H.. 33. 38 47. 28 'TotalVsaturated butane in stabilizer charge B A. 18. 32 29.01

A esin stabi lzer charge B. P. H 15.06 18. 27 Saturated butanes in feedto polymerization unit B, l. E: l0. 14 13. 76 Unsaturated butylenes infeed to polymerization unit l.- l H".- 7- 02 9- S5 Saturated-butanes tostabilizer bottoms n.1?. `6.73 11.04 Unsaturated but es to stabilizerbottoms B. P. H 5. 78 4. 25 'Percentage of available saturated butanesto- Feed to polymerization unit 55. 35 47. 43 Stabilizerbottdp1s 36. 7438. 06 Percentage of available unsaturated butyienes to? Feed topolymerization unit 46.61 53. 91 Stabilizer bottoms 38. 38 23. 26Overhead gas from stabilizer accumulator drum B. P. H 7.14 2A 09Eroznthe above, it will be noted that with substantially the same highpressure steam supply to the stabilizer reboiler and substantially thesame reboiler Vapor temperature, and with approximately the same coolingwater temperature for the stabilizer overhead condenser, very materialadvantages were secured with the butane recycle and injection into thereboiler of the stabilizer. Thus, the percentage of available butyleuesleft in the stabilizer bottoms dropped from approximately 38% to 23%,while the percentage of available butanes left in the bottom-s wasincreased from approximately 37% to 38%, and the Reid vapor pressure ofthe stabilized bottoms was maintained or even slightly increased from10.1 to 10.5 pounds, Moreover, the percentage of available butylenes inthe feed to the polymerization unit was increased from approximately46.5% to 54% while the percentage of available saturated butanesdecreased from approximately 55.5% to 47.5%. At the same time, there wasa substantially increased condensation of the stabilizer overhead andconsequently an increase in the charge to the polymerization unit, 'asis shown by the drop in the overhead gas from the accumulator drum trom7.14 to 2.99 barrels per hou'r.

It is thus seen that, by the method of the present invention, the rawcracked naphtha was stabilized to desired Volatility and Reid vaporpressure while at the same time a substantially improved separationbetween saturated butanes and unsaturated butylenes was secured so thata greater proportion of the saturated butanes remained in the stabilizedcracked naphtha while a greater proportion of the unsaturated butyleneswas removed overhead, condensed and thus recovered for thepolymerization feed. These beneficial results were secured solely byrecycling the available butane fraction from the polymer debutanizer tothe stabilizer reboiler, and without otherwise altering the conditionsof operation including high pressure steam supply to the reboiler ortemperature of cooling water to the stabilizer overhead condenser.

While the invention has been described above in connection with apolymerization unit, it is to be understood that the invention is alsoapplicable to other conversion processes for converting low-boiling ornormally gaseous hydrocarbons to high octane gasoline hydrocarbonssuitable for aviation fuel. Likewise, while the invention has beendescribed in connection with 'the stabilization of raw cracked naphthato obtain a separation between saturated butanes and unsaturatedbutylenes, it is to `be understood that the invention is also applicableto eiecting a desired separation between pentanes and @mylenes, hexanesand hexylenes, etc.

Referring to Fig. 2, the invention is shown as applied to thestabilization of raw cracked :Raphtha and natural gasoline and thealkylation of isobutane with C4 and C5 olefins to thereby materiallyincrease the yields of aviation gasoline from available charge stocks.As shown., raw cracked naphtha from a conventional cracking unit isintroduced by line 60 to stabilizer il equipped with reboiler 62, andoperated to take overhead by line 63 a C5 and lighterfraction-ccntaining a substantial proportion of the Cs olefins. Astabilized cracked naphtha containing a substantial proportion of normalpentane for volatility is withdrawn as bottoms byline 5.4. The overheadfraction is passed through con.- denser 65 to accumulator 66. Condensate.is forced by pump 01 in part through line. 63 to serve as reflux intower 6|, and in part by line 69 to a depropanizer 10. In the latter,the charge is fractionated to remove overhead through line 1l C3 andlighter, and obtain a bottoms cut consisting essentially of C4 and C5.which` is passed by pump 12 through line 13 to a conventionalalky-lation unit 14.

While any conventional alkylation process `can be employed, theinvention is described for purposes of illustration in connection withasulfuric acid alkylation step. In this process, an additional supply ofisobutane introduced by the recycle line 15 to be hereinafter furtherdescribed, or from any other suitable source, is mixed with the olefinicCi-Cs charge from line 13 in the presence of strong sulfuric acid ofabout {Z8-100% concentrationat temperatures of about 35-70 F. and undersufcient pressure-to main.- tain the hydrocarbon in liquid phase.Any-con, ventional type of unit, such as the Well known pump and timetank reactor, the jet reactor, or the mixer of the turbo type can beused. The isobutane is maintained in substantial molar excess of theolens; and preferably the operation is of the well known emulsionrecycle type in which contact ratios of from 50:1 up to 200:1 or higherare employed. Under these conditions, the isobutane is alkylated by theC4 and Cs ole.- iins to produce good yields of gasoline hydrocarbons oralkylate of high anti-knock value. Itis to be understood that other wellknown alkyl7 ation catalysts, such as hydrouoric acid, aluminumchloride-hydrocarbon complex, BFs-water complex, and the like can beused; although strong sulfuric acid is preferred for this operaE tion.As the alkylation unit per se forms no part of the present claimedinvention, further de, scription thereof is unnecessary. It isunderstood that in conventional practice, a stream of the reactionproducts is withdrawn to a suit, able settler where the catalyst isseparatedvfrom the hydrocarbons, and the latter are then `neu, tralizedbefore being passed to the stabilizing'and fractionating equipment.These various4 steps and the equipment therefor are well. known. and itis to be understood that the diagrammatic illustration of the alkylationunit represented by the numeral 14 includes the alkylation reactor,settler and neutralizer.

The neutralized hydrocarbon reaction products from the alkylation unitare passed by line 11 to a debutanizer 18 where unreacted -Cl hy,-

drocarbons 'consisting essentially of excess isobutane and normal butaneare removed overhead by line 'I9 and a debutanized alkylate is withdrawnas bottoms by line 8U. As the alkylation reaction consumes the olens inthe charge, the overhead C4 stream is further fractionated in a butanefractionator 80' where an isobutane out is removed overhead and recycledby line 'l5 to the alkylation unit while a normal butane stream isremoved as bottoms by line 8| and passed in whole or part by pump 82through line 83 to the stabilized cracked naphtha in line 6d to increasethe yield and volatility of the motor gasoline.

The debutanized alkylate withdrawn by line St is passed by pump 85through a line 85 to a depentanizer 81 where C5 is removed by theoverheadline and depentanized alkylate is removed as bottoms by line 89.It is to be understood that the above-described order of towers can bechanged. For example, the raw alkylate can first be depentanized, andthe resulting C5 and lighter oftgases fractionated in a series of towersto obtain the various fractions described, including an isobutane cut, anormal butane out, an isopentane cut and a normal pentane cut. The C5overhead fraction consisting essentially of isopentane and normalpentane is mixed with a stream of debutanized natural gasolineintroduced by line 90, and the mixture passed into a. de-isopentanizer9|. The latter is operated to remove isopentane overhead by line S2, andthe de-isopentanized natural gasoline containingthe normal pentane fromthe alkylate is removed as bottoms by line 93. The latter is passed bypump 9d to a depentam'zer 95 where normal pentane is removed overhead byline 96 and the depentanized natural gasoline discharged as bottoms byline 91. It is to be understood that the fractionating towers 10, 18,80', 8'lrand 9| are equipped with the usual reboilers or other heatingmeans for the base of the towers, and with suitable condensers andaccumulators for the overhead and pumps for supplying condensate as reuxto the tops of the towers as well as forcing the remaining portion ofthe condensate to the next tower or unit in series, which elements arenot shown for simplicity in illustration.

The overhead normal pentane fraction passes by line 9E to condenser 99and thence by rundown line to accumulator |0| from which condensate iswithdrawn through line |02 by pump I 03 and forced in part through reuxline |04 to the top of tower 95, and in part by recycle line I 05 to thereboiler B2 of the cracked naphtha stabilizer 6 I. In this manner, asaturated C5 stream consisting largely of normal pentane is provided forinjection into stabilizer 6| to thereby obtain a. more completeseparation of C5 olens in the overhead, while retaining a desiredproportion of normal pentane in the stabilized cracked naphtha bottoms.While the above described introduction of debutanized natural gasolineinto the fractionating system is advantageous for the production of moreisopentane, itis to be understood that this is not essential inaccomplishing the broader objects of the present invention. For example,the Cs cut from the stabilization of the alkylate may be directlyfractionated into isopentane and normal pentane fractions, Withoutaddition of any natural gasoline cut.

The depentanized alkylate removed from tower 81 by line 89 is forced bypump |01 through line |08 to the alkylate fractionator where a desiredaviation gasoline fraction boiling up to about S50-375 F. is removedoverhead by line Il and .gasoline from line Y l0 alkylate bottoms aredischarged by line and forced bypump ||2 through line H3 to storage orfor further treatment. Preferably, theA alkylate bottoms are passed byline ||3 to suitable blending tanks (not shown) where they are mixedwith the stabilized cracked naphtha from line 64 to increase the yieldofv motor gasoline. The overhead aviation fraction is condensed incondenser ||5 and passed through rundown line ||6 to accumulator l fromwhich the aviation gasoline is discharged by line |`|8 -to storage orfor further treatment. The overhead isopentane fraction from line 92 ispassed to suitable condenser and accumulator equipment (not shown) andthe condensate' blended with the aviation |'|8 to thereby increase theyield and adjust the volatility of the -aviation gasoline. Itis to beunderstood that the depentanized natural gasoline from line 91 may, ifdesired, be passed to a further fractionating tower (not shown) servingas a de-isohexanizer from which an overhead isohexane cut may beobtained for blending with the aviation gasoline from line ll 8 tofurther increase the yield thereof. The resulting natural gasolinebottoms from this further fractionating operation may then be passed toreforming or other treatment, or may be blended directly with thestabilized cracked naphtha from line 6d for motor gasoline.

It is to be understood that the debutanized natural gasoline introducedby line 9D has been previously stabilized to separate C4s and lighter,and the oigases from this stabilization fractionated to separate an isintroduced by line |2l into theisobutane feed for the alkylation unit 74to thereby serve as an external source of supply of additionalisobutane. A normal butane also recovered from, the natural gasoline inthis latter operation may be added to the normal butane stream passed byline 83 to the stabilized cracked naphtha in line 64. These elements arenot illustrated in the drawing for the sake of simplicity inillustration.

While the invention has been described above combination with a suitablepolymerization alkylation unit, from which the desired recycle stream isobtained for injection into the cracked naphtha stabilizer, it is to beunderstood that the. invention is not limited to these particularcatalytic conversion units. Thus, it is obvious that the stabilizationmethod described herein can be applied in conjunction with othercatalytic or thermal conversion units, such as isomerization,cyclization and aromatization, and various `combinations of these withpolymerization and alkylation. Likewise, the invention is not limited tothe stabilization of cracked naphtha and natural or straightrun gasolinefractions, since the particular stabilization and fractionation methodis more broadly applicable to the distillation of olen and paraincontaining hydrocarbon mixtures generally.

The invention can also be employed in a stabilizing operation where theoverhead condensate capacity is insuicient for normal operation, tothereby enable the stabilizer to operate at a higher pressure for thesame reboiler temperature, with resultant increased condensation of theoverhead at the higher pressure with the same condenser cooling surface.Likewise, the invention can be applied to stabilizing operations wherediiiiculty is encountered due to the temperature of available coolingWater for the overhead condensate being too high, since the higherstabilizer pressures resulting from the hydrocarisobutane-rich fractionwhich bon injection permit increased overhead condensation with the'higher temperature cooling Water. r'

Obviously `many modifications and .variations ofthe invention, asherein'before set forth', may be rmade Without *departing .from thespirit.` and scope thereof; and thereforeionlysuch limitations should beVmade as are indicated in' the' appended claim.

I claim:

The method in the stabilization of a raw cracked naphtha,and the'manufacture of gasoline, hydrocarbons of high anti-knock value' from theoverhead of the stabilizing operation, wherein the C4 hydrocarbons of4the rawcracked naphtha consist of substantial proportions each ofisobutane, normal butane', is'obutylene, butylene-l and butylene-Z'; andthe proportion of thebutylene-z in saidi fraction, is. roughlyequivalent to the combined; proportion of isobutylene and butylene-1,which "comprises introducing the .raw cracked naphtha intol anintermediate portion of a'stabiiization andrectic'ation zone', heatingthe-lower portioniof said zone tovaporizeC4` and lighter vconstituentsby indirect heat exchange with a heating'medium, subjecting the overheadfrom 's aidzone to cooling andondensation at the 'pre'ssure'ofV saidzone by'indii'ect'v heat exchange with a cooling" medium; returning 'aportion ofthe 'resultingfcondensate as reflui'rlto anlupper portion ofsad zone, 'the'operationibeing lsuch that a portion of 'the C4'.together 'with lighterV constituents passes overheadironi. said zonewhile' `a stabilized Ycracked 'naphtha containing sufiicient C4 'to meetvolatility specifications is ldischarged as bottoms, 'subectinganl otherportion' Loffsai'd overhead condensate to catalytic' conversion" tolargely" convert' butyl'enes thereof 'into 'high `anti-'knockl`lgasoline hydrocarbons While 'ri-buta'ne'M of-"s`a`id`overh'adcondensate remains inert, *separatingiifni tl' 'products' ofsaid'catalytic conversin' said Ag'asolilr'e hydrocarbons, also`separatin'gfl f'o'ii th'ef pluts of said catalytic c'oriv'ersion'a Ci:fraction conssting mainlyof n-butane, and` recycling` 'said C4 45consisting niainly'l of n-but'ane" to the iract'io'n I K 0i SL21@etebilizeltoaantl realisatie@ interior zone in,.sufcient 4proportion inrelation .to .the Iraw .cracked .naphtha Ifeed. to accormlilish .thefollowing Athree results, .namely iCl) materially increasathepressure insaid zone iora.given temperature :in the t lowerporton of said. zone,(2) materially increase ithe lcondensation `ofrroverfi head vapors fromsaidfzone for.a\.givenitemper ature ofthe cooling. medium supplied,thereto, and (3) materially increasefthe combined'rproportionofrisobu-tylene, butylene-l .and butylene- 2 taken overhead forv akgiven retention oi G4 including ifi-butane in .the stabilized Acrackednaphtha bottoms to meet volatility specifications. LOREN- P. SCOVILLE.

REFERENCES.. crrnn.

The following reerences arcor recom' in the file of this'patent:

Uurrn s'rnfrns ammira Diagrammatic Flow Sheet in the. Renner, Oct.1942,- vol. 211, between-.pages 140. and: 141.

Burrell, The VRecoveryv of. Gasolinev -from NaturaLGasf? 1925;pagesaandz46.

Applications. ot rEhe'rmal Pol Oil'-` andi Gas Jour.; June.22, 1989,pages-A52', 53', 66 and; 69f72 (pages.531andJlOtpertinent)

